Risk of subsequent cytological abnormality and cancer among women with a history of cervical intraepithelial neoplasia: a comparative study.

A longitudinal study of 1,281 women with a histological diagnosis of cervical intraepithelial neoplasia (CIN) during 1974-76 is presented. After 12 years of follow-up, 30 percent of the women had further cytological abnormalities reported. The rate of subsequent abnormality was highest during the first 12 months of follow-up; thereafter, there was no evidence of any decline in the rate of subsequent abnormality with increasing duration of follow-up. Women from the CIN cohort had twice as many later cytological abnormalities as an age-matched cohort of women who were negatively screened during 1974-76 (excluding abnormalities within 12 months of entry to the study and after adjustment for smear frequency). The CIN cohort remained at substantially greater risk for a subsequent diagnosis of squamous cell carcinoma of the cervix compared with the control group of negatively-screened women (rate ratio 19.8, 95 percent confidence interval 2.4-163.6, P less than 0.01). These results indicate that women who have received surgical intervention for CIN continue to have substantial morbidity from cervical abnormalities during medium-term follow-up.